Delay of cell cycle progression after X-irradiation of synchronized populations of human cells (NHIK 3025) in culture.

The effect of X-irradiation on the cell cycle progression of synchronized populations of the human cell line NHIK 3025 has been studied in terms of the radiation-induced delay of DNA replication and cell division. Results were obtained by flow cytometric measurement of histograms of cellular DNA content and parallel use of conventional methods for cell cycle analysis, such as pulse labelling with [3H]thymidine and counting of cell numbers. The two sets of methods were generally in good agreement, but the advantages of employing two independent techniques are pointed out. Irradiation was found to have a minor influence on DNA replication. As compared with unirradiated populations, half-completed DNA replication was 20--30 min delayed in populations 580 rad in mid-G1 or 290 rad in early S. Cell cycle progression was markedly delayed in G2. The sensitivity induction of this delay was 0.6 min/rad for populations irradiated in mid-G1, and 1.4 min/rad for populations irradiated in early S.